The present invention relates to hydrophones, more particularly to methods and apparatuses for arraying plural hydrophones for acoustical purposes.
Hydrophone staves (synonymously referred to herein as acoustic sensor staves) are an integral part of an HGA (high gain array) system that is used for acquiring submarine-radiated noise measurements at sea. Hydrophone staves were developed by the NSWCCD (Naval Surface Warfare Center, Carderock Division) Signatures Directorate, and were initially deployed on the NSWCCD's HGAs. This “potted” stave design, currently in use by NSWCCD, incorporates twenty individual cylindrically shaped acoustic sensors and twenty U-shaped preamp (preamplifier) board assemblies. Each acoustic sensor and preamp unit is separately encapsulated (i.e., potted) in polyurethane. These units are assembled onto a cable conductor bundle with a central Kevlar strength member, and are spaced at equal distances from each other along the cable bundle axis. The conductors and strength member are passed through the center of the acoustic sensor, and the preamp assembly is attached adjacent to each acoustic sensor by placing the cable bundle through the open portion of the U-shaped preamp. The conductors associated with each acoustic sensor are then cut, and jumper wires are soldered, to make the necessary connections between preamp, acoustic sensor and cable bundle. Each hydrophone assembly, which includes a sensor and a preamp, is secured to the cable bundle by encapsulating the unit in a polyurethane material.
The potted hydrophone staves described in the preceding paragraph were first built and deployed in 1993. Since that time, these staves have experienced numerous failures, mostly involving water intrusion through the outer jackets of damaged conductors. Due to the design of the potted hydrophone staves, repair of malfunctioning hydrophones proved to be very difficult, and in many cases impossible. Among the inherent design limitations of these staves are the following: the polyurethane encapsulant is subject to deterioration from sunlight and saltwater; the small sizes of the conductors are associated with exposure to kinking/breaking during deployment/retrieval/storage cycles; the outer jacket of the conductors is the only barrier from water penetration; a damaged hydrophone cannot be efficiently repaired or replaced, and therefore an entire stave of twenty hydrophones must be replaced in order to have a one hundred percent operational stave.
Since NSWCCD's initial deployment of the potted hydrophone staves, many design improvements have been incorporated into the building of some newer potted hydrophone staves that replaced some older ones; nevertheless, hydrophone failures due to water intrusion have continued to cause long-term reliability problems. As a consequence of the above-noted problems associated with the conventional potted hydrophone staves, an engineering endeavor was initiated in October 1997 to develop a more robust stave design that would greatly improve reliability and could be easily repaired if necessary. The present invention's non-kinking, “oil-filled” acoustic sensor stave is a result of this design initiative.
Generally speaking, oil-filled hydrophone staves are devices that are known and used in the acoustic community. Typically, these staves each include an array of phones that are mounted at fixed ends. An oil-filled hydrophone stave is made to contain a liquid material (e.g., Isopar or castor oil) mainly for the purpose of matching the acoustic impedance of the ambient seawater. The U.S. Navy as well as petroleum/oil exploration companies frequently use oil-filled hydrophone arrays in towed array applications. Nevertheless, like the known potted hydrophone arrays and staves, the known oil-filled hydrophone arrays and staves are not as robust as desired in certain handling and storage operations (e.g., are subject to stave kinking) and are characterized by a degree of difficulty in terms of assembly and repair. What is needed is a hydrophone stave that represents an improvement in these problem areas while still meeting the high performance acoustic requirements of the hydrophone stave in an ocean environment.
The following references, incorporated herein by reference, are examples of United States patents that are pertinent to hydrophones, hydrophone staves and/or hydrophone arrays: Skinner U.S. Pat. No. 6,208,584 B1 issued Mar. 27, 2001; Dvorsky et al. U.S. Pat. No. 5,894,651 issued Apr. 20, 1999; Brenner et al. U.S. Pat. No. 5,499,219 issued Mar. 12, 1996; Flanagan et al. U.S. Pat. No. 5,220,538 issued Jun. 15, 1993; Jackett et al. U.S. Pat. No. 4,862,428 issued Aug. 29, 1989; Anderson U.S. Pat. No. 4,745,584 issued May 17, 1988; Rogers et al. U.S. Pat. No. 3,982,144 issued Sep. 21, 1976.